The Yakhchal: Background information when reading Chilled

The Yakhchal

This article relates to Chilled

Long before the advent of the refrigerator, around 400 BCE, the ancient Persians had figured out a way of making ice and having it readily available even over the summer. At its most basic, the solution took advantage of the low humidity and cool desert nights, especially in winter, to make ice and then store it in an insulated building called the yakhchal all through the summer months. The yakhchal, quite a few of which are still standing today, are tall structures that look like inverted ice cream cones or spinning tops.

Persia used a qanat system of irrigation which is essentially a gently sloping system of channels, situated underground, used to divert water from aquifers as needed. To make the ice, each yakhchal had a series of tunnels into which water from the yakhchal was funneled pretty much every night during the winter. High walls positioned to protect the freezing water from wind and other atmospheric disturbances, were constructed. The shadows cast by these walls further accelerated the freezing process. As the ice froze in layers, it was harvested and stored away in blocks once it reached a thickness of about 50 cm. Interestingly, the ice was not stored in the yakhchal domes but in huge pits dug into the ground. Below ground was cooler so ice was packed here with layers of insulation such as straw and sawdust.

Since it was just as important to store the ice as it was to make it, a series of design prerequisites maximized insulation. The thick walls of the yakhchal (two meters at the base and less as one traveled up) were made with a mortar comprising sand, clay, egg whites, lime, goat hair and ash. While the insulating properties of egg whites and lime are largely open to debate, it is believed that the goat hair served a function much like today's fiberglass in fiberglass insulation. Small steps were carved into the outside of the yakhchal so workers could climb its walls and cover the structure with thatch to prevent external elements from disturbing the contents. Water sprinkled or even poured over the outside would evaporate, further cooling the contents and keeping things relatively stable. A series of wind-catchers would also essentially "fan" the structure, keeping things cool, and "small holes were cut into the apex of the dome to release the warm air rising up from inside," Jackson explains in Chilled. Special trenches at the bottom of the yakhchal quickly funneled away any melted water (which would otherwise accelerate the melting process) and divert it to the trenches to be frozen again.

Probably because the manufacture of ice was not easy, it was only for the rich, who used it generously to make sharbats (iced drinks with cordials) and faloodeh, a popular dessert across much of the Middle East (and South Asia) that uses noodles, rosewater, basil seeds and plenty of crushed ice. Interestingly, in modern Farsi, the word for a refrigerator is yakhchal.

A Yakhchal in Iran, courtesy of Pastaitaken
The inside of a qanat, courtesy of NAEINSUN
The inside of a Yakhchal, courtesy of Slick-o-bot
Faloodeh, courtesy of MathewTownsend

Filed under Cultural Curiosities

This "beyond the book article" relates to Chilled. It originally ran in October 2015 and has been updated for the October 2016 paperback edition. Go to magazine.